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Wednesday, March 25, 2015

Argentine Cactus is Yellowing

Q. I have two quite large Argentine Giant cactus, each
with many pups they've offset from their base. They are both located on a West
facing patio, one is in a large pot and the other is planted in native soil. The
one in the pot always turns yellow on its south side this time each year. The
one in the ground does not. The potted one has been in that pot for about seven
years, and I generally give it fertilizer a couple times a year. I think I've even tried a bit of iron, though
I don't really think that is the problem.

A. The usual reason for this cactus becoming a yellowish
in color is sun damage, particularly if it only on the side facing the sun.
Other possibilities could be the buildup of salts in the soil, lack of
nutrients, root damage and cold damage. But the bottom line is stress.

Because the cactus has a
restricted root system and has no ability to take water from deeper or
surrounding soils, the plant may be more stressed in a container than the one
planted in the ground. That's how I would view it.

The yellowing is resulting
from stress. I think the plant in the container will stress more easily than
the one in the ground. This cactus will turn yellow (side facing the sun) in a
stressful microclimate when planted in the ground.

You should consider all of these
as possibilities but I think it is most likely sun damage or bleaching of the
plant tissue by intense sunlight. They will do a little bit better without so
much intense sunlight, particularly the one in the container.

All that being said, make sure
that the soil has adequate drainage and you are not watering too often so that
you can eliminate root damage because of the soil kept too wet.

Choose a good fertilizer for it.
I like Cactus Juice as a fertilizer for cacti and succulents. I've had a lot of
good reports from people using this fertilizer on them.

When you water it next time make
sure you add enough water so that a good 20% of the water applied comes out the
bottom holes or moves past the roots to keep the salts flushed.

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Home. My home base is Las Vegas, Nevada, in the Eastern Mojave Desert. This blog focuses on horticulture in Deserts.

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